1. Field of the Invention
The present invention relates to the manufacture of integrated circuit (IC) chips, and in particular to the packaging of chips at the chip level. At the same time, packaging of chips relates to chip bonding, including the current wire bonding, to Chip Scale Packaging (CSP) test fixture concerns, and the attendant reliability concerns.
2. Description of the Related Art
Packaging of IC chips determines to a large extent the performance of the system of which the chips are the smallest building blocks. As-one chip must communicate with one or more other neighboring chips in order to perform a system function, the method by which the chips are packaged and interconnected makes a difference in their speed of communication. For example, current mini-BGA (Ball-Grid-Array) packages using wire bonding as interconnection are not as effective in high frequency circuit applications. Also, chip scale packaging (CSP) is important in determining the type of fixtures that must be used for testing. It is disclosed later in the embodiments of the present invention a CSP package and a method of manufacturing the same which substantially improves the performance of the IC chips as well as the testing cost of the chips.
As is known in the art, integrated circuits are formed on a silicon wafer which is then diced or cut to form individual die, also called chips. The circuits which are interconnected in each chip terminate at terminals on the chip. The appropriate chips are then interconnected with each other by bonding those terminals onto a card having its own interconnections. Depending upon the complexity and function of the final machine that is to be built, this first level package may in turn be interconnected with other first level cards by connecting the cards onto a second level package, usually called a board.
The chip level interconnection forming the first level package is usually performed using wirebonding (WB), tape automated bonding (TAB), or flip-chip solder connection, sometimes referred to as controlled collapse chip connection (C4). A detailed description of each of these interconnection schemes will not be given here so as to not obscure the key aspects of the present invention, and also, as they are not necessary to the understanding of the teachings of the present invention.
A conventional first level mini-BGA package, (10), is shown in prior art FIG. 1. The die, or chip (20) is wire-bonded (40) to substrate (30), which in turn is connected to second level package (70) through solder connections (60). The mini-BGA package Ls always encapsulated in a molding material (50). It will be known to those skilled in the art that it would be desirable to eliminate wires (40). Such a method is disclosed later in the embodiments of the present invention. Some other prior methods of making connections to chips are disclosed in U.S. Pat. Nos. 5,994,766 by Shenoy et al., 6,118,183 by Umehara, et al., 6,137,164 by Yew et al., 5,734,201 by Djennas et al, and 5,914,533 by Frech et al., where they use redistribution layers. Lau, on the other hand, shows a low-cost surface mount compatible land-grid array (LGA) chip scale package (CSP) for packaging solder-bumped flip chips. Higgins also discloses a CSP mounted to a substrate using direct chip attach (DCA) method.
The present invention, as disclosed later, differs from prior art in that a CSP is formed by integrating a redistributed chip on a substrate. The I/O solder balls are first mounted through the substrate vias, which in turn are connected to the chip I/O pads. The substrate is attached to the chip by an adhesive.